1. Field of the Invention
This application relates to an optical signal generator, and more particularly to an optical signal generator that generates various types of optical modulation signals.
2. Description of the Related Art
An optical time division multiplex (hereinafter, referred to as “OTDM”) technique, which is a signal multiplexing technique suitable for an optical transmission system capable of transmitting a great deal of data fast, is well known. With the OTDM technique, optical signals transmitted in multiple channels are multiplexed into one signal with a predetermined wavelength by switching the channels at regular time intervals.
A polarization time division multiplex technique is also well known in relation to the OTDM technique. With the technique, optical signals in two lines are separately modulated and the modulated optical signals are multiplexed by changing a polarization state of one of them. Japanese Patent Laid-Open No. 2001-36505 discloses an optical signal generator using the polarization time division multiplex technique.
However, the aforementioned optical signal generator can generate only a signal multiplexed by the polarization time division multiplex technique. That is to say, the generator is unable to generate signals modulated by techniques other than the polarization time division multiplex technique.